(a) Field of the Invention
The present invention relates to a handover method in a next-generation mobile communication system. More specifically, the present invention relates to a handover method applicable to the AII-IP based network, a next-generation mobile communication system.
(b) Description of the Related Art
Rapid developments and diversification in the information technology industry have caused many users to require various services, and hence, next-generation mobile communication systems that fluently provide high-speed mobile multimedia services are also needed. Accordingly, the next-generation mobile communication systems support AII-IP network environments as a default so as to support very high-speed radio packet transmission technologies and have flexibility with links to the existing Internet.
The conventional 3rd generation mobile communication system includes circuit-switched networks, and the next-generation mobile communication networks include packet-switched IP (Internet protocol) networks.
FIG. 1(a) shows a configuration of a RAN (radio access network) in the AII-IP mobile communication network, and FIG. 1(b) shows a protocol configuration between a terminal and a base station.
As shown in FIG. 1(a), the RAN comprises an AS (access station) for functioning as an access point, and an AR (access router). The AS matched with the base station of the conventional mobile communication system executes a control function over an air interface, a radio resource management function, a mobility management function, a call management function, and a packet scheduling function. The AR executes an IP packet routing function and a mobile IP function.
FIG. 1(b) shows a user plane protocol configuration between a base station and a terminal in the next-generation high-speed multimedia mobile communication system. User traffic is on the basis of IP-based data transmission. A user IP is allocated from an AS or an AR having a foreign agent function by a mobile IP. A PDCP performs a header compression function of the IP packets, and an RLC (radio link control) layer performs radio link control functions including data flow control and reliable data transmission. A MAC (media access control) layer performs traffic scheduling and packet multiplexing, and a physical layer has the OFDM technology applied to data transmission in the air interface.
The most important factor in the IP-based mobile communication system is a terminal's mobility. A mobile IP is used to guarantee the mobility of the terminal. The mobile IP allocates a new IP address (i.e., a CoA (care-of-address) hereinafter) for enabling communication in a moved area when the terminal has moved to a new network or cell, and it binds a terminal-specific IP to a CoA for each network, thereby solving the above-noted mobility problem. A basic mobile IP processing procedure is described below, a registration process is shown in FIG. 2, and a tunneling process is shown in FIG. 3. Referring to FIGS. 2 and 3, a mobile IP processing procedure will be described.
1. Agent Discovery
When receiving an agent advertisement message periodically advertised by an MA (mobile agent), a mobile node 22 (also referred to as a mobile terminal) of FIG. 2 analyzes the received message, and performs a registration process when the mobile node belongs to a foreign network 2.
2. Registration
When a terminal sends a registration request message to an FA (foreign agent) 21, the FA 21 sends the registration request message to an HA (home agent) 1 to perform a registration process on the corresponding terminal 22. When the HA 1 updates a home address of the mobile terminal and a mobility binding table 11 of the CoA after an authentication process is finished, and sends an acknowledgment message to the FA 21, the FA 21 updates terminal information and sends a response message to the mobile terminal 22.
3. Service
1) When a CN (correspondent node) 31 sends packets to the home address of the mobile terminal, the HA 32 receives the packets and transmits them to the FAs 21 and 33 through a tunnel.
2) The FAs 21 and 33 use a visitor list 211 to search whether a target terminal of the received packets is provided on the current network, and when it is on the list, they transmit the packets to the corresponding terminal.
3) When the mobile terminal transmits the packets to the CN 31, the mobile terminal initially sends the packets to the FAs 21 and 33, and the FAs 21 and 33 route them according to a normal IP routing method.
As described in the process summary of the mobile IP, in order for a mobile terminal to move to a foreign network to register a location, and receive a CoA, it is required for an HA and an FA to communicate messages between them. Therefore, if the handover frequently generates because the mobile terminal frequently changes access networks, the message exchanges frequently occur, and this occurrence may work as a load on the whole network. Also, each time the handover occurs, it is problematically required to update the routing table and the mobility binding table in relation to the HA and the FA, and a processing delay for reconfiguring the IP layer becomes longer. In addition, in the case of updating an IP connection, a remarkable amount of packets are lost in the break-and-make process. That is, the mobility support method of the mobile IP has 3 problems. First, it takes much time to update information on the HA and the FA and receive a new IP. Second, messages for updating the information may increase loads on the network. Third, data may be lost in the handover process.